We cannot find published data on the yearly average rainfall specific to the Pu Ngaol village. However, plenty of weather apps available online may provide this information. Consider broadening your scope (i.e. looking at the commune, district or Mondulkiri province as a whole) or even looking at the weather of the capital city of Mondulkiri province, Sen Monorom. For example, this website by the Ministry of Water Resources and Meteorology is a reliable source used by the locals and Cambodian expats when checking the daily weather forecast.
If you want to learn more about Cambodia’s rainfall patterns and water supply, this recent ADB report is a good read.
Lastly, check this section of the design brief: Introduction to Cambodia context, to gain more background information about the Pu Ngaol village.